In solar system, though the cost of the cable is not high, as the "blood vessel" of the pv system, it plays an important role in connecting pv modules, inverters, distribution boxes and the grid, and also plays an important role in the operation safety of the whole system, which even influences the overall profitability of the power station. Therefore, the cable selection in system design process is very critical.   1. Types of pv cables From the perspective of different functions, the cables in the pv system can be mainly divided into two types: DC cables and AC cables.   1.1 DC cable ① Serial cables between pv modules. ② Parallel cables between strings and between strings and DC distribution box (combiner box). ③ Cables between the DC distribution box and the inverter. The above cables are all DC cables, and they are often laid outdoors. They need to be protected from moisture, sun exposure, cold, heat, and ultraviolet rays. In some special environments, they also need to be resistant to chemical substances such as acids and alkalis.   1.2 AC cable ① Connecting cables from the inverter to the step-up transformer. ② Connecting cables from the step-up transformer to the power distribution unit ③ Connecting cables from the power distribution device to the power grid or users The above cables are all AC load cable, which are often laid in the indoor environment, and can be selected according to the general power cable selection requirements.   2. Why choose dedicated pv cable? Under much circumstance, DC cables need to be laid outdoors. The cable materials should be determined according to the resistance to ultraviolet rays, ozone, severe temperature changes and chemical erosion. The long-term use of ordinary material cables in this environment will cause the cable sheath to break and even decompose the cable insulation layer. These conditions will directly damage the cable system, and will also increase the risk of system short circuit. In the medium and long term, the possibility of fire or personal injury is also higher, which greatly affects the lifespan of the system. Therefore, it is very necessary to use dedicate pv cables and modules. Solar-specific cables and modules not only have the best weather resistance, UV and ozone resistance, but also can withstand a wider range of temperature changes.   3. Principles of cable design and selection ① The withstand voltage of the cable should be greater than the maximum voltage of the system. For example, for AC cables with 380V output, 450/750V cables would be selected. ② For the connection inside and between the system arrays, the rated current of the selected cable is 1.56 times the maximum continuous current in the calculated cable. ③ For the connection of AC loads, the rated current of the selected cable is 1.25 times of the calculated maximum continuous current in the cable. ④ For the connection of the inverter, the rated current of the selected cable is 1.25 times of the calculated maximum continuous current in the cable. ⑤ Consider the influence of temperature on the performance of cable. The higher the temperature, the less the current carrying capacity of the cable, and the cable should be installed in a ventilated and heat-dissipating place as much as possible. ⑥ Consider that the voltage drop should not exceed 2%.   4. The DC circuit is often affected by various unfavorable factors during operation and causes grounding, which makes the system unable to work. Such as extrusion, poor cable manufacturing, unqualified insulation materials, low insulation performance, DC system insulation aging, or some damage defects, can cause ground faults or become a grounding hazard. In addition, the intrusion or biting of wild animals in the outdoor environment will also cause a DC ground fault. In this case, armored cables with rodent-proof functional sheaths are generally necessary.   5. Summary: Select the appropriate cable according to the grid form supported by inverter and data of the maximum continuous current in the cable.

In a power system, power is generally sent from the grid to the load, which is called forward current. After installing a photovoltaic power station, when the power of the pv system is greater than that of the load, the power that cannot be consumed will be sent to the grid. Since the current direction is opposite to the conventional one, it is called “countercurrent".   1. What is anti-backflow? An usual photovoltaic power generation system converts AC to DC. When the power of the photovoltaic system is greater than that of local load, the extra electricity will be sent to the grid. The photovoltaic system with CT(Current Transformer) has anti-backflow function, which means that the electricity generated by photovoltaics is only supplied to loads, preventing excess electricity from being sent to the grid.   2. Why do you need anti-backflow? There are several reasons for installing an anti-backflow prevention solution: 2.1.Limited by the capacity of the upper-level transformer, users have new grid system installation needs, but it is not allowed locally. 2.2.Due to some regional policies, grid connection is not allowed. Once it is found, the grid company will impose a fine. 2.3.The pv panels have been installed, but due to incomplete filing information (such as unclear real estate property rights, etc.), the grid company does not allow grid connection, and the cost of installing energy storage systems is very high.   3. How to achieve anti-backflow? Install an meter or a current sensor at the grid-connected point, and feed back the detected grid access point data to the inverter. When it detects that there is current flowing to the grid, the inverter responds quickly and reduces the output power until the countercurrent is Zero, so as to achieve zero power Internet access.   4. The solution? Deye inverter anti-backflow working principle: install an meter with CT or current sensor at the grid-connected point. When it detects that there is current flowing to the grid, it will feed back to the inverter, and the inverter will immediately change its working mode and track from the maximum power point of MPPT. The working mode is transferred to the control output power working mode, and the output power of the inverter is nearly equal to the load side, so as to realize the anti-backflow function. According to different system voltage levels, photovoltaic anti-backflow systems can be divided into single-phase anti-backflow systems, three-phase and energy storage system ones.

How to calculate solar panel efficiency?   Let us take the SAIL SOLAR 550W solar panel as an example and calculate the module efficiency. PV module power (Pmax in watts) ÷ PV module surface area in square meters = 550W / (2.279m * 1.134m) / 1000 =21.3%   What is solar cell efficiency? Solar cell efficiency refers to the energy efficiency with which a solar cell converts it into electricity through photovoltaic technology. Also take the SAIL SOLAR 550W as an example. SAIL SOLAR 550W is made of 182mm solar cell ( dimension: 182*91mm). 144cells. 550W/144=3.82W per cell 3.82W/(0.182m*0.091m)/1000= 23.1%   Why is there a difference between solar panel efficiency and solar cell efficiency? Compared to the example of the SAIL SOLAR 550W mentioned above, solar cell efficiency is 23.1%, while solar panel efficiency is 21.3%. The reason for this difference is that cell efficiency calculations refer to individual cell, while solar panel efficiency refers to the entire solar panel module. Some energy is lost due to the spacing between solar cells. Similarly, the bus bar on the solar panel is also covered on the surface of the cell. The thinner the bus bars, the less efficiency is lost to the solar panel. Moreover, the shadow of the bus bar on the cell will also affect the efficiency. For example, the thickness of the bus bar of a 5-bar solar cell is 0.4mm, while that of a 9-bar solar cell is 0.1mm. This also leads to a difference between solar panel efficiency and solar cell efficiency.   In fact, other raw materials used to produce solar panel, such as glass, EVA, junction boxes, etc., will also have a certain impact on efficiency.   Then, there's the "fill factor," often abbreviated as FF, which is a measure of how close a solar cell is to being an ideal light source. This is a key parameter for evaluating performance. It can be simply understood that this parameter is used to determine the maximum power from the solar cell.

Shadows should be paid attention to in the design and installation of photovoltaic power plants, and more attention should be paid to later operation and maintenance. For long-term operation of photovoltaic power generation systems, dust accumulation on panels has a great impact on power generation efficiency. The dust on the surface of the panel has the functions of reflecting, scattering and absorbing solar radiation, which can reduce the transmittance of the sun, resulting in a decrease in the solar radiation received by the panel, and the output power is also reduced, and its effect is proportional to the accumulated thickness of dust. Common shadows mainly include bird droppings, dust, tree shade, buildings, fallen leaves and branches, etc. At present, there are three cleaning methods for photovoltaics: human working, water wheel cleaning and robot cleaning. 1.      Characteristics of human working Hard to manage, inefficient, and long hours. The cleaning process affects power generation. The cleaning quality is difficult to guarantee, and there are safety risks and large losses in operation. 2. Water wheel cleaning The cleaning range is limited, and it is only suitable for ground power stations with sufficient space and free entry and exit of vehicles. It won't do anything with rooftop photovoltaic panels, desert power stations, or tightly packed power stations. 3. Robot cleaning Regular cleaning, significantly increased power generation, night work, no impact on power generation, more than 50 times more efficient than human working, self-powered, self-storage, no external energy, unattended, intelligent control, no water cleaning, no waste of water resources.